by
Tham Chee Keong
Plantation Officer
Forests Department
Sabah
INTRODUCTION
Several species of Acacia have been introduced into Sabah since 1950. They are Acacia auriculiformis, A. holosericea, A. richii, A. confusa and A. mangium. Of these, only A. mangium has shown potential for timber production.
Acacia mangium was introduced from Mission Beach, Queensland in 1966 to Ulu Kukut Forest Reserve, Sabah and planted as a firebreak species. At Ulu Kukut, it competes well with Imperata cylindrica grass. Subsequently, it has been planted widely in sites with low fertility colonised by Imperata grass.
NATURAL DISTRIBUTION AND HABITAT
According to Pedley (1964) the natural occurrence of this species stretches from Aru Island in the Moluccas Group; Wuroi, Oriomo River in the Western Division of Papua down to Northern-Eastern Queensland between Ingham and the Diantree River.
In Queensland, A. mangium occurs on margins of mangrove communities and rainforests in coastal districts (Pedley, 1978). Little is known about its habitat in Papua and Moloccus.
PERFORMANCES AS AN EXOTIC IN SABAH
The species has been widely grown in Imperata grassland with degraded soil. It also grows well on disturbed sites such as tractor paths, road cuttings, abandoned shifting cultivation areas, etc.
In a 10-year old plot at Sibuga Forest Reserve, trees planted at 2.4 m × 2.4 m spacing attain an average overbark D.B.H. of 20 cm and mean height of 23 m. The overbark volume up to 10 cm top was measured to be 439 m3/ha, i.e. a MAI of 44 m3/ha/yr.
Being a legume, the roots have an abundance of nitrogen fixing nodules. An ectomycorrhizal fungus of the Thelephora genus is also associated with the roots.
Like other Acacia species, the seedlings of A. mangium are often attacked by meal bugs and grasshoppers in the nursery. Such attacks are less common in the field. Isolated incidences of attack by a defoliating beetle, Hypomesus squamosus, have been observed.
Acacia mangium trees are extremely sensitive to Grammoxone and Dalapon. Spraying with these herbicides results in the shedding of leaves and die-back of shoots. The trees generally recover if the concentration of chemicals is low.
CROWN AND STEM FORM
A. mangium is a vigorous species with relatively good form. The canopy closes one year after planting. It can grow up to 30 m tall with a bole of 25 cm D.B.H. The main bole is usually straight with slight fluting. Branches are small and horizontal; frequently self-pruned.
HYBRIDISATION
A. mangium and A. auriculiformis growing in close proximity hybridise naturally as there is an overlap in the time of flowering between the two species. Hybridisation results in progeny of various forms and growth. Observations indicate that hybrid vigour is found in some progenies which, however, tend to inherit the poor form of A. auriculiformis.
WOOD PROPERTIES AND USES
The narrow sapwood, straw to creamy white in colour, is distinct from the light brown heartwood. Grain is straight on the tangential face and slightly interlocked on the radial face. Texture is medium. The air-dried density is 624.7 kg/m3.
The timber can be sawn easily, planed to a smooth surface and polished well. It is probably suitable for general construction purposes, and for furniture, boxes and crates. Tests have indicated that the timber can be treated by the full-cell pressure impregnation method with a satisfactory loading and penetration of preservative.
Samples collected from 8-year old trees produced good ribbon-type particle board. At the time of writing, pulp and paper tests are being carried out. So far, results seem to indicate that the wood yields pulp of a satisfactory quality.
CONCLUSIONS
Acacia mangium has proved to be a successful competitor to Imperata cylindrica grass. This is an advantage in Sabah as there are substantial areas of former shifting cultivation land which have been abandoned and are now colonised by Imperata grass. Coupled with the facts that seeds are readily available and the timber properties are good, it is likely that large areas will be planted with the species in Sabah.
So far, most of the Acacia mangium planted in Sabah derive from one single tree in Mission Beach, Queensland. Small quantities of seeds have also been introduced from Ingham and Mossman, Queensland. The genetic pool of Acacia mangium in Sabah is thus relatively small. To date, no studies have been made on the performance in Sabah of Acacia mangium from Papua and the Moluccas Islands. It is imperative that comprehensive provenance trials and tree improvement work be carried out in the very near future before large areas are planted with Acacia mangium. Assistance from international organizations such as FAO/UNDP and IUFRO would facilitate collection of seeds in the natural habitats of the species.
REFERENCES
Pedley, L. 1964 Notes on Acacia, chiefly from Queensland. I. Proceedings of the Royal Society of Queensland. Queensland Herbarium, Botanic Gardens, Brisbane.
Pedley, L. 1978 Austrobaileya, Volume I, No. 2. Queensland Herbarium, Department of Primary Industries, Brisbane.
 | Photo 1. 4-month old A. mangium seedling. Pinnate juvenile leaves near base. | |
 | ||
Photo 2. A. mangium roots with Thelephora mycorrhiza and nitrogen fixing nodules. | ||
 | |
 | |
Photo 3. 2-year old A. mangium on left, Eucalyptus deglupta of the same age on the right. | |
Photo 4. 6-year old A. mangium regenerated after fire. Ulu Kukut, Sabah. |
